Calibration pressure - 28" or much higher?

[larrycavan]

Been watching this thread with interest....I have to 3rd Bruces motion...

I think it's as simple as this. By the time you get a pipe that's large enough to not screw wth the Cd of the orifice, you've effectively created a plenum anyay...may as well start right there, use the spredsheets available here and get practically unlimited support for a KNOWN bench type if you run into trouble...

I'm not saying it won't work. It's reallly about simplicity. There is no better application for the KISS principal than a flowbench...I can assure you of that..

JMO [sincerely hope I'm not stepping on anyone's toes with this opinion - I do admire the effort put into anyone's engineering project and frequently learn new things from them]

[Stef]

SWR:
If you want formulea to calculate Cd values, Google Reader-Harris/Gallagher equation and Stoltz equation. These are the current formulas used by ISO and ASME standards.

Bruce:
The reason I've been looking at using an orifice in a pipe is because that is where they are mostly used. Because of that, it's where most of the data about orifice plates come from and which most standards for flow measurement using orifices are based. Having worked in the process industry before where orifices in piping runs are common, I naturally tended towards it.
But, having spent many hours on this forum and reading the posts on the old forums too, I can see your (and others) points of view. Using two large plenums, one either side of the orifice, is appealing and simple too. If you look at the standards you can also see that arrangements with a large Beta ratio, as you would get with a plenum arrangement, have stable Cd values down to very low flow rates.
One of the good things about this forum is that other peoples experiences can make you think "outside the box" and re-evaluate your ideas.

Stef

[bruce]

[SWR]

Ok guys,
I get it.

Reason for putting the orifice in a pipe was two-fold: 1: I have almost unlimited access to industrial,dual-sealed circular ventilation ducting/bends/T-tubes/whatever in every size from about 3" to 20",lots of billet alu/SS bar and a lathe for making orifices...

So,I just used the KISS principle and thought there would be no easier way than that. :p Had I known that it would be practically impossible to make "my" type of orifice bench work accurately,I would not have done it this way.

2: I was told that the orifice in a pipe was just as accurate as doing it any other way,as long as the pipe diameter was at least 1.5" bigger each side than the orifice hole. (i.e. 2" hole,5" pipe). Obviously, (hindsight is such a nice thing!) I was all wrong.

The next question would then be... what kind of pitot or flow meter would you stuff inside the pipes I have? I've spent several weeks constructing the thing,so I'd like to use it as it is for now,(except for the fact that I want it to work,of course! ) until I "get the need" to improve or go bigger later.

[larrycavan]

[bruce]

[1960flh]

[color=#000000]Not to over simplify this but to pick up on as Bruce said the never stop learning. Please don

[Thomas Vaught]

Laminar Flow Element is not a orifice plate in a true sense.

It is a fine cell matrix, much like a catalytic converter on your automobile.

The cells dispurse the flow into literally hundreds or thousands (depending on the diameter of the lfe) of individual passages.

A Delta Pressure is measured on either side of the individual passages.

LFEs require a very clean environment, may be damaged by foreign material hitting the LFE matrix, and are expensive.

Orifice benches and pitot tubes are less expensive, less maint, and can be very accurate. Typically LFEs need a valid calibration curve for the unit as it is a "single range" instrument.

JMO

Tom V.

[1960flh]

Thanks Tom;

This clarifies it for me, as my question came from examples (Sketches) I have seen on the net and in older Physics books. My Assumption was that it could not be that simple but I have never had one in my hand to be able to investigate the design.

[Tony]

[jsa]

[color=#000000]1960flh,

[quote]but isn

[SWR]

I'll just try a few things that Bruce told me to try with my setup,if it doen't work I'll go with his averaging pitots.